Direct Evidence for Solid-like Hydrogen in a Nanoporous Carbon Hydrogen Storage Material at Supercritical Temperatures

(Graph Presented). Here we report direct physical evidence that confinement of molecular hydrogen (H₂) in an optimized nanoporous carbon results in accumulation of hydrogen with characteristics commensurate with solid H₂ at temperatures up to 67 K above the liquid-vapor critical temperature of bulk H₂. This extreme densification is attributed to confinement of H₂ molecules in the optimally sized micropores, and occurs at pressures as low as 0.02 MPa. The quantities of contained, solid-like H₂ increased with pressure and were directly evaluated using in situ inelastic neutron scattering and confirmed by analysis of gas sorption isotherms. The demonstration of the existence of solid-like H₂ challenges the existing assumption that supercritical hydrogen confined in nanopores has an upper limit of liquid H₂ density. Thus, this insight offers opportunities for the development of more accurate models for the evaluation and design of nanoporous materials for high capacity adsorptive hydrogen storage.